In recent years, in electrical equipment, various resin molded items have been used in housings and internal electrical system components. Examples of electrical equipment include not only typical household electrical appliances and industrial electrical appliances, but also, for example, equipment controlling the electrical systems in vehicles such as automobiles, motorcycles and trucks, and resin molded items are also widely used in this type of electrical equipment. For electrical equipment used inside vehicles, and particularly for resin molded items used in equipment disposed inside engine rooms, items capable of withstanding corona discharge caused by the ignition coils or the like are required. In other words, when a resin molded item is exposed to a corona discharge, a tree-shaped localized failure known as an electrical tree develops and shortens the lifespan of the resin molded item, and this must be prevented.
On the other hand, because resins used in electrical equipment inside vehicles also require heat resistance and flame retardancy and the like, polyarylene sulfide resins (hereafter also referred to as “PAS resins”) that exhibit the required performance are often used. However, on their own, PAS resins do not provide sufficient corona resistance, and therefore various proposals have been made for imparting resin molded items (compositions) with corona resistance (for example, see Patent Documents 1 to 3).
Patent Document 1 discloses a material (a biaxially oriented film) formed from a polyphenylene sulfide (hereafter also referred to as a “PPS resin”) in which the corona resistance has been improved by ensuring that the sodium chloride content is not more than 0.5% by weight.
Further, Patent Documents 2 and 3 disclose molded items (a cable component and a snow adhesion-resistant ring) formed from resin compositions containing a PAS resin, a conductive carbon black, graphite and an epoxy group-containing α-olefin-based copolymer. These items aim to provide corona resistance, in addition to various other properties such as heat resistance, weather resistance, flame retardancy, water repellency, airtightness and toughness, by setting the volume resistivity of the resin composition to an appropriate value.
The resin compositions (molded items) disclosed in Patent Documents 1 to 3 are able to provide a corona resistance effect of at least a certain level, but the corona resistance is not entirely satisfactory, and there remains room for further improvement.
On the other hand, resin compositions containing a PAS resin and also containing a silicone-based polymer such as a polysiloxane for the purpose of improving various properties of the resin composition are also known (for example, see Patent Documents 4 to 6). The resin composition disclosed in Patent Document 4 is designed to obtain superior water repellency, the resin composition disclosed in Patent Document 5 provides improved flame retardancy, and the resin composition disclosed in Patent Document 6 is designed to obtain superior mechanical strength and chemical resistance. In other words, none of the resin compositions disclosed in Patent Documents 4 to 6 aims to provide corona resistance. Currently, no composition is known that provides improved corona resistance by combining a PAS resin and a silicone-based polymer.